Synthetic foundry sands



Patented Dec. 16, 1947 SYNTHETIC FOUNDRY SANDS Burgess P. Wallace, NewYork, N. Y.

N Drawing. Application April 4, 1946, Serial No. 659,670

6 Claims. (Cl. 22-188) This invention relates to the production ofsocalled synthetic molding and facing sands.

The principal objects of the invention comprise the expeditious andeconomical production of products of the aforesaid character, all ofwhich are adapted to effectively prevent the fusion of sand particles inthe surfaces of molds contain ing such products with the metal thatcontacts with such surfaces during a metal casting operation. Otherobjects of the invention are hereinafter set forth.

As I am well aware, it has been proposed in Patent No. 2,348,155 toproduce mold-facing sand by mixing together in the cold, sharp orunbonded sand, bentonite, pitch and sea-coal, preferably in theproportions of approximately 80% sand, 12% bentonite, 12% pitch and 4%sea-coal.

In such a mixture since the bentonite is directly admixed with the sand,as distinguished from being completely isolated therefrom by aheat-insulating layer of fine sooty carbon such as is the case with myimproved facing sand, as hereinafter described, the usual objectionablefusion would occur between the sand particles in the forming surfaces ofa mold containing such mixture and the metal in the surface of a castingproduced by such mold since the directly admixed bond will promote suchfusion.

My investigations hav led to the discovery that it is not essential thatthe carbon particles in sands such as aforesaid shall be of solid carbonthroughout, but that the same may consist of nuclei of unbonded or sharprefractory particles coated with a fine layer or film of hydrocarbonscontaining a pre-determined amount of soot-producing substances whichupon contact with molten metal substantiall completely decompose to afine soot composed of colloidal carbon that serves to smoke those partsof the mold which would ordinarily be inaccessible to facing mate rials.

I am well aware that it is common practice to admix sea-coal withmolding sand in order to accomplish the aforesaid purpose,namely, theproduction of gaseous hydrocarbons which on decomposition when exposedto the heat of the molten metal produce an atmosphere of soot in themold, but due to the fact that such sea-coal is mechanically admixedwith the molding sand and also has been applied as a thick layer overthe pat tern during the formation of the mold, a considerable portion ofthe sea-coal is wasted since only the portions thereof on the surface ofthe mold will be decomposed by the molten metal on contact therewith andthe balance of the sea-coal embedded in the mold, which constitutes themajor portion thereof, will'be wasted,

At the present time foundry sands, such as aforesaid, whether the samebe natural or artificial, usually consist of sand particles surroundedby a thin coating or layer of a colloidal clay-like substance whichserves as a bond, 1. e., it causes the sand particles to adhere to eachother and thereby form a suitable molding medium. When molten metal,heated .to temperatures ranging from about 1445 C. to 1750 0.; strikessuch said particles, the clay bond surrounding each particle acts as aflux and tends to lower the normal melting point of the silica, about1700 C., with the result that both the silica particle and the bond fuseto the metal. resulting in a badly burnt-in casting. The higher thetemperature of the metal the greater the degree of fusion which occursand consequently the worse the resultant burnt-in sand condition. Thiswill be more readily appreciated by a considera tion of the resultsobtained in casting various metals in sand molds. For example. whenaluminum and magnesium are cast, due to the relatively low temperaturesat which they are poured, ranging from about 700 0., there will besubstantially no burnt-in sand condition observable. In the case ofvarious brasses, poured at 1200 0., some burnt-in sand condition willoccur. In the case of both iron, poured at 1445" C. to 1535 C., andsteel, poured at 1650 C. to 1750 C. the burntin condition is verypronounced and decidedly objectionable and the higher the temperatureabove these ranges the worse such burnt-in condition becomes, due to themore extensive nature of such fusion of the clay or other bondingmaterial to the metal and the sand particles. This burnt-in conditioncan, I have discovered, be substantially prevented if the bondingmaterial be separated from the sand or silica particles by somecombustible carbonaceous material, in which event although the incomingmetal will fuse the clay bond nevertheless, due to the simultaneouscombustion' of the carbonaceous material lying beneath the clay bond,the latter will be temporaril separated by a gaseous or sooty envelopeboth from the silica particle and from the metal. Hence the silica,being separated from the flux or bond, will not fuse and by the time thecombustible separating layer is completel consumed so much heat willhave been dissipated from the metal in the mold that it will havesolidified and consequently will be no longer capable of picking up thefused clay. Th resultant casting will, therefore. be substantially freefrom burnt-in sand or-clay.

As a preferred example of the method of making my improved molding,facing or core sands, I preferably proceed as follows:

200 parts of sharp sand free from any bond, desirably of about 70 mesh,are introduced into a suitable mixing chamber, such as that of a. batchmixer or a continuous tubular mill. Powdered coal tar, urea or likecombustible hydrocarbon is then introduced into said mixing chamberdesirably in the ratio of one part thereof to twenty of the sharp sandor silica, employed. The actual amount of the combustible materialemployed depends upon the fineness of the silica base, as the finer thebase the greater will be the surface area to be coated and consequentlythe more combustible material that will be required. Following thecharging of the combustible material into the mixing chamber, the chargeis heated sufficiently to melt the pitch or like combustible employedwhile continually stirring r agitating said charge. Then the mass isallowed to cool and is then pulverized to any desired degree offineness, desirably about 70 mesh. It is then in condition to be shippedto foundries which are accustomed to bond their own sand, but beforeshipping elsewhere it is desirably bonded to the requisite extent,depending on the character of the work to be performed therewith byintimately incorporating bentonite therewith, desirably bentonite of 250to 350 mesh fineness.

Other refractory bases which may advantageously be employed in additionto those above set forth, are zircon sand, kaolin, fly ash and stackdust. In fact almost any refractory base fusing above about 650 C. issuitable, provided it is not objectionably chemically active.

For the carbon-producing or soot-yielding component of my improvedsynthetic molding sand products, I preferably use coal tar pitch asabove stated, but other substances such as asphalt, gilsonite,rosin-pitch, anthracene oil and naphthalene are excellent substitutestherefor since all of them readily decompose and yield voluminous sootyfumes when contacting molten metal heated about 650 C.

As set forth in the technical work by Herbert Abraham entitled Asphaltand Allied Substances, fifth edition, 1945, vol. 1, published by D. VanOstrand, Inc., the fusion point of coal-tar pitch ranges from about 80F. to 300 F. or even higher,

I ber of the group consisting of a solid. a semithat of asphalt, bothnatural and residual petroleum asphalts, between 80 F. and 225 F. (seepages 405 and 496 respectively), that of gilsonite between about 270 F.and 400 F. and that of rosin pitch between about 100 F. and 200 F. (seepages 251 and 329, respectively).

Various changes in and modifications of the foregoing procedures andproducts, within the scope of the appended claims, may be made withoutdeparting from the spirit of my invention.

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. A synthetic foundry sand, comprising principally finely divided sandnuclei, which nuclei are free from bonding material, evenly coated witha heavy hydrocarbon belonging to a memsolid and a normally non-volatileliquid and capable of yielding voluminous soot-like fumes on contactwith molten metal during a casting operation and clay-like bondingmaterial externally deposited on said coated nuclei.

2. A foundry sand comprising principally silica nuclei, free frombonding material, evenly coated with asphaltic material and capable ofyielding voluminous sooty fumes on contact with molten metal during ametal casting operation and claylike bonding material externallydeposited on said coated nuclei.

3. A sand for use in molding operations in foundries, comprisingprincipally silica nuclei, free from bonding material, evenly coatedwith a pitch-like hydrocarbon capable of yielding voluminous sooty fumeson contact with molten metal during a casting operation; and bentoniteexternally deposited on said coated nuclei.

4. In the method of making a sand for molding operations in foundriesthe steps comprising evenly coating finely divided refractory materialwhich is infusible below about 650 C. and which is free from bondingmaterial with a heavy hydrocarbon belonging to a member of the groupconsisting of a solid, a semi-solid and a normally non-volatile liquidand capable of yielding voluminous sooty fumes on contact with moltenmetal during a casting operation and then finely comminuting theresultant product and admixing therewith a minor proportion ofbentonite.

5. In the method of making a molding sand. the steps which compriseevenly applying to particles of sharp molding sand a coating of a heavyhydrocarbon belonging to a member of the group consisting of a solid, asemi-solid and a normally non-volatile liquid and capable of yieldingvoluminous sooty fumes on contact with molten metal during a castingoperation and then finely comminuting the resultant product and adding aminor proportion of bentonite thereto for bonding the same.

6. A molding sand comprising principally sharp sand whose individualparticles are evenly coated with pitch-like material and which coatedparticles are surrounded by bentonite particles externally depositedthereon.

BURGESS P. WALLACE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,758,095 Wallace May 13, 19302,256,456 Dietert Sept. 16, 1941 2,322,638 Kleeman June 22, 19432,322,667 Seastone June 22, 1943 2,348,155 Shanley May 2, 1944 FOREIGNPATENTS Number Country Date 535,561 Germany Oct. 12, 1931

